The objective of this research proposal is the improvement of medical ultrasound image quality via a new generation of piezoelectric, two- dimensional array transducers, using the technology of multi-layer materials. Our hypothesis is that we can develop more sensitive, higher frequency, less expensive two-dimensional transducer arrays with a larger number of active channels by using multi-layer materials than with conventional transducer technology. These new, more sensitive transducers will increase the depth of penetration and enable the use of higher frequencies to improve the spatial resolution in every clinical application of medical ultrasound. The 1 1/2-D and 2-D array transducers of this proposal have become absolutely essential for the improvement of diagnostic ultrasound imaging for applications in obstetrics, cardiology and radiology. Unfortunately, there are three obstacles which limit such transducer arrays including: fabrication difficulties, low transducer sensitivity, the requirement for many hundreds of active transducer channels. The application of multi- layer polymer and multi-layer polymer and multi-layer ceramic materials to ultrasound transducers will solve these problems. Our specific aims are: 1) To investigate the application of multi-layer polyimide connectors to solve the fabrication problems of 1 1/2-D and 2-D arrays. 2) To continue our investigations of multi-layer PZT, for more sensitive 1 1/2-D arrays intended for B-scan imaging of the breast and abdomen. The arrays will consist of as many as 4 x 64 = 256 elements operating at frequencies up to 7.5 MHz with individual element sizes as small as 0.1mm in width. 3) To continue our investigation of multi-layer PZT, for more sensitive 2- D arrays intended for real time volumetric scanning of the heart and abdomen. The arrays will consist of as many as 80 x 80 =6400 elements at frequencies up to 5 MHz with element sizes as small as 0.2mm on a side. 4) To explore the use of very low impedance 1 1\2-D arrays (approx. 10 omega/element) and very low impedance integrated circuit (IC) transmitters along with IC preamplifiers within the transducer itself to further increase SNR and improve image resolution. 5) To investigate 1 1\2-D arrays intended for breast scanning using a new transducer material, i.e., multi-layer piezoelectric composites.